High-performance heat sinks produced from die-cast aluminium alloys

Topic of the month

Cooling solutions such as heat sinks, electronic housings, high-density liquid heat sink plates and similar must have specific properties for heat dissipation.

This also includes a high level of thermal conductivity, low porosity, leak tightness and the ability to be able to construct thin walls and high fins.

The CTX partner company, Aavid Thermalloy, developed the high density die casting (HDDC) process in collaboration with university partners. The technology allows the manufacturing of near-net shaped parts with better mechanical and thermal properties compared to traditional die-cast elements.

The process is especially suitable for the manufacture of high-performance heat sinks and liquid heat sink plates made from aluminium alloys with a high thermal conductivity. The new and innovative process control during the solidification process provides a fine grain structure with almost zero porosity.

Copper, graphite or other solid materials which have lower thermal expansion coefficients than aluminium can be embedded directly within the cast part.

The process creates a loadable mechanical connection - which has almost no porosity whatsoever or gaps between the surfaces. Surface characteristics such as fins, bosses or recesses match the respective electronic components and the fixation technology.

Thin lamellas with a high side ratio

HDDC-heat sinks have numerous important advantages compared to processed, die-cast or extruded heat sinks. The higher thermal conductivity - coupled with more diverse possibilities when it comes to the configuration of lamellas, thickness and shape - are unique advantages, for example, in the case of pen-shaped elliptical or radial cooling lamellas.

Many of these properties cannot be achieved through extrusion or traditional die-cast technologies. The process also allows the manufacture of electronic housings with cooling fins which are significantly lighter due to their thinner walls and have elaborate characteristics.

The extreme density, pore-free quality of the cast part of the HDDC cooling elements allows reworking processes such as machining, brazing and welding to be used, which in turn allows complex and leak-free modules to be realised.

The surfaces of the HDDC heat sinks are so smooth and dense that following wet surface treatments such as anodising and galvanising, no electrolytes can penetrate the metal.

• Even temperature distribution: 3D lamellas and cooling channels, as well as improved geometric properties such as reduced wall thickness, smaller gaps between the cooling lamellas and thinner cooling lamellas as well as a reduced draft angle optimise the flow paths and ensure an even temperature.

• Large-volume production: Just like die-casting, the HDDC process is suitable for the large-volume production which includes prefabricated inserts made of copper, stainless steel or other metals for the thermal distribution or inserts with threads for valves or fluid connections.

• Absolutely secure: For the production of absolutely tight liquid heat sink plates, the parts made from AL 6XXX-alloys can either be simply brazed or CAB can be used.

An effective cooling is decisive for the correct functioning and long service life of modern high-performance electronics. It is for this reason that certain criteria need to be considered when selecting the ideal cooling solution.

The type of cooling solution is decided upon by taking the space and installation conditions depending on the power dissipation of the component to be cooled. These parameters determine whether a passive cooling with natural convection is sufficient or if the extent of the power dissipation makes active cooling with fan assistance a necessity. If an improved cooling is still not sufficient, liquid cooling will be used.

With the type of cooling, the criteria for the design of the heat sink change. In the case of natural convection, the surface must be as large as possible. There must be sufficient distance between the cooling fins, and the materials (aluminium and/or copper) must have a high level of thermal conductivity.

The improved convection requires an additional heat sink design, which eliminates air-turbulences for example. Liquid-cooled cooling solutions place high demands on the tightness of the entire system, amongst other things.

"When the construction space available and the power dissipation allow it, for reasons of long-term reliability and costs, the decision should be for a cooling solution using natural convection", explains Wilfried Schmitz, Managing Director of CTX, which is regarded as the leading retailer with an exceptionally broad and varied product range of heat sinks.

The product range covers small heat sinks for SMT applications through to the large liquid heat sink plate. This means that CTX has the suitable solutions to a wide variety of problems and provides its customers with comprehensive support when selecting the respective cooling solution.